As a fuse assembly, there is known a fuse assembly that comprises a hollow casing, a pair of spaced apart electrodes mounted to the casing, and a fuse link or fuse element disposed within the casing and bridged between the spaced apart electrodes. In such a fuse assembly, when an overcurrent, which ranges from several ten times to several hundred times larger than a rated value, flows through the fuse link, the fuse link is partially melted and then cut into two parts, and the current is resultantly cut off. At this time, an arc discharge is generated between the parts of the melted fuse link.
As the two parts of the fuse element are melted by heat generated due to the arc discharge, a gap between the two parts of the melted fuse element becomes larger. As a result, the arc discharge will be spontaneously extinguished. Also, it is well known to persons skilled in the art that if an alternating current source is employed as a power supply for associated electrical equipment, the arc discharge tends to easily extinguish at the time when an AC voltage becomes zero.
Moreover, there is known a fuse assembly including a case filled with arc-extinguishing medium such as quartz sand. In this case, when an overcurrent flows through a fuse element of the fuse assembly, the fuse element is partially melted and then cut into two parts, and an arc discharge is generated, metal vapor which is produced from melted metal of the fuse element heated due to the arc discharge is then deposited on the quartz sand. As a result, the arc discharge is cooled and then extinguished.
However, in the event of the fuse assembly being small-sized, it is hard to cause the arc discharge to be extinguished since an entire gap between electrodes of the fuse assembly is inevitably small and the fuse element is inevitably shorter. Therefore, in order to cause the arc discharge to be positively extinguished, a fuse element that is long in length is inevitably required, so that an entire fuse assembly inevitably becomes larger. However, such a fuse assembly is practically inconvenient, since it can not comply with demands on miniaturization of associated electrical equipment. Moreover, in a case where applied voltage is high, even if such a fuse element is employed, the arc discharge tends to continuously occur. Also, in a case where a direct current source is employed as a power supply for associated electrical equipment, voltage does not become zero, so that there is less chance of extinguishing of the arc discharge.
When the generation of the arc discharge is continued and the metal vapor is continuously produced from the melted fuse element, there is a possibility that the casing of the fuse assembly will be burst or the electrodes are blown since an internal pressure in the casing is elevated by the continuous metal vapor. In addition, there is a possibility that arc heating will bring about internal ignition of the casing and the arc discharge will bring about flashover. As a result, the associated electrical equipment will be finally damaged.
Meanwhile, it is well known to persons skilled in the art that when the metal vapor from the melted fuse element progresses and the internal pressure in the casing is increased, shock waves are generated in the casing. The inventor aimed at this fact and experimentally found that it was possible to cause an arc discharge to be positively extinguished by controlling the shock waves.